The invention is directed to a process for the recovery of pure L-cystine from a mixture with other aminoacids by fractional crystallization in the presence of acids and water.
It is known to separate cystine from a mixture of aminoacids by fractional crystallization. To separate the cystine, especially from tyrosine, the crystallization takes place from dilute aqueous hydrochloric acid with addition of sodium acetate (Org. Syntheses 5 (1925) 39-41). Cystine also is separated from tyrosine and leucine by crystallization from concentrated aqueous hydrochloric acid and from glutamic acid in neutral aqueous medium (German Pat. No. 907,175). The disadvantage of these processes is that a pure cystine free from tyrosine can be produced only with considerable expense or with moderate yields.